1. Field of the Invention
The present invention relates to force-feedback input devices, and in particular, relates to a unit for optimizing a damping force of a damping-force-feedback input device which applies to an operating unit a returning force according to an operating position of the operating unit and the damping force in proportion to an operating speed of the operating unit.
2. Description of the Related Art
A force-feedback input device including an operating unit manipulated by an operator, a detecting unit for detecting the operational state of the operating unit, a force-feedback unit for providing a force feedback to the operating unit, and a controlling unit for controlling the operation of the force-feedback unit based on detection signals output from the detecting unit so as to provide a predetermined force feedback according to the operational state of the operating unit to the operating unit has been used in practical applications as an input device applicable to, for example, a bi-wire central controlling unit for automobile-installed electrical equipment, a steering device, a gearshift device, and a braking device. The force-feedback input device controls the operation of the force-feedback unit in the controlling unit and provides to the operating unit a force feedback, for example, a feeling that the operating unit touches a wall (referred to as a wall-touching sensation hereinafter), according to the operating position of the operating unit.
As disclosed in Japanese Unexamined Patent Application Publication No. 2003-150261, several types of force-feedback input device have been proposed: a type which provides to the operating unit a proper resistance during the operation of the operating unit and a type which provides an additional force feedback in proportion to the operation speed of the operating unit. This provides an operating unit with a superior operating feeling.
One example of the force feedback according to the operating position of the operating unit, namely, a force feedback in proportion to the movement of the operating unit rather than a force feedback having a constant magnitude regardless of the movement, is called an elastic force. A force feedback in proportion to the operation speed of the operating unit is called a damping force and is obtained by multiplying the operation speed of the operating unit by the damping coefficient. Since the damping force provides a resistance similar to viscous friction when operating the operating unit, the damping force may be called a viscous frictional force.
FIG. 4 is a block diagram of a type of a force-feedback input device which was proposed by the present inventor. This force-feedback input device mainly includes an operating unit 1 manipulated by an operator, a detecting unit 2 for detecting the operational state of the operating unit 1, a force-feedback unit 3 for providing a force feedback to the operating unit 1, and a controlling unit 4 for controlling the operation of the force-feedback unit 3 so as to provide to the operating unit 1 a predetermined force feedback according to the operational state of the operating unit 1.
The controlling unit 4 includes an operational-state-calculating subunit 4a for calculating the movement θ and the operation speed θdot of the operating unit 1 based on detection signals output from the detecting unit 2, a returning-force-calculating subunit 4b for calculating a required returning force Te(θ) according to the movement θ of the operating unit 1, a damping-force-calculating subunit 4c for calculating the damping force c·θdot in proportion to the operation speed θdot of the operating unit 1, and a resultant-force-calculating subunit 4d for calculating the resultant force Te(θ)−c·θdot derived from the combination of the returning force Te(θ) and the damping force c·θdot. The controlling unit 4 controls the operation of the force-feedback unit 3 based on the signals output from the resultant-force-calculating subunit 4d so as to provide a required force feedback to the operating unit 1.
Referring to FIG. 5, the operation of the known force-feedback input device having the above-described structure when an encoder is used as the detecting unit 2 will now be described.
When power is supplied to the controlling unit 4, in step S11 the controlling unit 4 counts the number n of signal pulses output from an encoder, i.e., the detecting unit 2, for a predetermined time Δt. In step S12, the controlling unit 4 calculates the movement θ of the operating unit 1 based on the equation θ=θ+n and calculates the operation speed θdot of the operating unit 1 based on the equation θdot=n/Δt in the operational-state-calculating subunit 4a. In step S13, the controlling unit 4 calculates the returning force Te based on the equation Te=k(θ−θ0) when θ0≦θ≦θ1 or the equation Te=k(θ1−θ0) when θ1<θ in the returning-force-calculating subunit 4b and calculates the damping force Tc based on the equation Tc=c·θdot in the damping-force-calculating subunit 4c, where k is the elastic coefficient and θ0 is the base position of the operating unit 1 and c is the damping coefficient. When θ0≦θ≦θ1, an elastic force in proportion to the movement is provided. When θ1<θ, a constant force is provided. This constant force has the same value as the elastic force when θ=θ1. In step S14, the controlling unit 4 calculates the resultant force Ttotal of the returning force Te and the damping force Tc which is provided to the operating unit 1 based on the equation Ttotal=Te−Tc in the resultant-force-calculating subunit 4d. In step S15, the controlling unit 4 operates the force-feedback unit 3 based on the resultant force Ttotal output from the resultant-force-calculating subunit 4d, and a required force feedback is provided to the operating unit 1.
In the force-feedback input device having the above-described structure, the damping force Tc and the returning force Te are provided to the operating unit 1. Thus, a resistance is provided to the operating unit 1 and a superior operating feeling of the operating unit 1 can be achieved. When θ0≦θ≦1, the returning force is large in proportion to the movement, that is, the elastic force is provided so as to suppress oscillation at the position θ0.